use strict; 
use warnings; 
use Data::Dumper;

my $keep = 5;
my @keeper;

# populate our store with the first $keep vals
for (1 .. $keep) {
    my @vals = split /\s+/, <DATA>;
    my $score = pop @vals;
    push @keeper,  [$score, \@vals];
}

# Sort it so the smallest is at the end
@keeper = sort {$a->[0] <=> $b->[0]} @keeper;

print "$_->[0], " for @keeper;

while (<DATA>) {
    my @vals  = split;
    next unless @vals; # could do a more sophisticated test
    my $score = pop @vals;
    if ($score > $keeper[0]->[0]) {
        $keeper[0] = [$score, \@vals];
        @keeper = sort {$a->[0] <=> $b->[0]} @keeper;
        print "\nAdded $score: now have: ";
        print "$_->[0], " for @keeper;
    }
}

__DATA__
0 5 3 7   0.97
1 5 4 8   0.18
1 5 4 8   0.21
1 5 4 8   0.22
1 5 4 8   0.52
1 5 4 8   0.16
1 5 4 8   0.18
1 5 4 8   0.72
1 5 4 8   0.32
1 5 4 8   0.17
1 5 4 8   0.52
1 5 4 8   0.92
6 8 4 6   0.54
[download]

Cheers,
R.